Composite particles and method for production thereof and use thereof

ABSTRACT

A composite particle comprised of a larger particle and, supported thereon, smaller particles wherein the smaller particles are photocatalyst-containing fine particles with an average particle diameter of 0.005-0.5 μm as calculated from a BET specific surface area, and the larger particle has an average particle diameter of 2-200 μm as measured by the laser diffraction-scattering particle size measuring method. The smaller particle is preferably a composite particle of titanium dioxide with an inorganic compound exhibiting no catalytic activity, such as silica, or a particle containing a Brφonsted acid salt, especially on the surface thereof; and an advantageous method for producing the above composite particles wherein the above larger particles and smaller particles are dry mixed by a ball-mill or mixed by rotation of blades or by shaking, with an energy constant controlled within a specific range. A composition comprising an organic polymer and the above composite particles can give a shaped article, such as fiber, film or a molding, exhibiting ultraviolet ray-screening function.

TECHNICAL FIELD

This invention relates to a composite particle, a method for theproduction thereof, and use thereof.

The composite particle of the present invention comprises a largerparticle and, supported thereon, fine particles having a photo-catalyticactivity. The composite particle exhibits highly effectively aphoto-catalytic activity, and is useful as a structure, a shapedarticle, a film or a fiber which exhibit a photo-catalytic activity.

BACKGROUND ART

Many kinds of inorganic fine particles are known as having aphoto-catalytic activity. A most typical example of the inorganic fineparticles is titanium dioxide fine particles.

Titanium dioxide absorbs ultraviolet rays, and consequently, positiveholes and electrons are generated inside the fine particles. Thepositive holes react with water adsorbed in the titanium dioxide, andgenerate hydroxyl radicals, which has a function of decomposing organicmatter, adsorbed on the surface of titanium dioxide particles, intocarbon dioxide gas and water (see Akira Fujishima, Kazuhito Hashimotoand Toshiya Watanabe, Light Cleaning Revolution, published by C.M.C.1997). This function is referred to as photo-catalytic function.Titanium dioxide exhibits a strong photo-catalytic activity providedthat positive holes are easily generated and positive holes easilymigrate to the surface of titanium dioxide particles (see The Whole ofTitanium Dioxide Photocatalyst, edited by Kazuhito Hashimoto and AkiraFujishima, published by C.M.C. 1997). As titanium dioxide exhibiting astrong photo-catalytic activity, there can be mentioned anatase-typetitanium dioxide particles, titanium dioxide particles having reducedlattice defects, and titanium dioxide particles having a small particlediameter and a large specific surface area.

Most of organic matter can be decomposed by the above-mentionedphoto-catalytic function, and therefore, beneficial functions such asanti-fungus, self-cleaning, deodorizing and anti-staining functions canbe imparted, for example, to tiles, building materials, constructionalmaterials, fibers, films and other materials by allowing these materialsto support titanium dioxide particles on the surfaces thereof.

The above-mentioned photo-catalytic function is manifested on thesurfaces of titanium dioxide particles, and therefore, titanium dioxideparticles must be located on the surfaces of the materials or members towhich the beneficial functions are to be imparted. A simple and easymethod for this requirement includes a method of coating the material ormember with a composition comprising titanium dioxide and a binder.However, in the case when an organic high polymer is used as the binder,the binder is easily oxidized and/or decomposed by the photo-catalyticfunction. Therefore, a binder, which is not subject to decomposition,such as a fluororesin or a silicone resin, must be used (see JapanesePatents No. 2756474 and 3027739).

However, in the case when photo-catalytic semiconductor particles areused as a mixture thereof with a resin binder, the resin binder isliable to cover the surfaces of titanium dioxide particles and thus, theexposure of the photo-catalytic titanium dioxide-particles to light, andthe contact of the titanium dioxide particles with the material ormember to which the beneficial properties are to be imparted, areimpeded. Consequently a problem arises in that the photo-catalyticeffect of titanium dioxide is reduced. Further another problem arises inthat the resin binder must be cured by heating.

As for a composite particle comprising titanium dioxide particles,composite particles have been proposed for various purposes. Mostcomposite particles comprise a combination of a particle having a largerdiameter (hereinafter referred to as “Mother particle” when appropriate)with particles having a smaller diameter (hereinafter referred to as“child particle” when appropriate). The mother particle has a functionof manifesting the performance of child particles with an enhancedefficiency. In the case when there is no great difference in sizebetween two kinds of particles, fine particles having a desiredperformance are referred to as “child particles”, and particles having afunction of manifesting the desired performance of child particles withenhanced efficiency is referred to as “mother particles”.

For composite particles comprising titanium dioxide particles, most ofthe composite particles comprise titanium dioxide particles as the childparticles because titanium oxide particles exhibit various performancessuch as opacifying effect, photo-catalytic effect and ultravioletrays-screening effect. Mother particles used for the titaniumdioxide-containing composite particles are chosen so that the maximumeffect of titanium dioxide is manifested. As examples of the motherparticles for giving titanium dioxide-containing composite particles,there can be mentioned mother particles having a specific refractiveindex difference and a specific band gap in order to obtain the maximumultraviolet rays-screening effect of ultra-fine titanium dioxideparticles (Japanese Unexamined Patent Publication [hereinafterabbreviated to as “JP-A”] No. H11-131408, JP-A H9-100112 and JP-AH8-268707: silica mother particles in order to impart high transparencyfor the same purpose (JP-A 2000-344509); and calcium carbonate motherparticles for obtaining an enhanced opacifying effect of titaniumdioxide particles (JP-A 2002-29739). Further there have been proposedfinely divided inorganic particles having titanium dioxide supported onthe surfaces thereof by using an organic binder in order to enhance thephoto-catalytic activity of titanium dioxide (Japanese Patent 3279755);and aluminosilicate particles as the mother particles in order toprovide a composite particle exhibiting a photo-catalytic activitywithout deterioration of a resin even when the composite particle isplaced in contact with the resin(JP-A H11-76835). Further there havebeen proposed a method of mechanically combining mother particles withchild particles by a high-speed airflow impacting method (JapaneseExamined Patent Publication No. H3-2009 and JP-A H6-210152); and amethod of combining mother particle with child particles by a surfacemelting method (Japanese Patent No. 2672671).

Titanium dioxide has a catalytic activity and therefore its utilizationis restricted. That is, when an organic high polymer is used as abinder, the polymer is oxidized and decomposed by the action of titaniumdioxide. Even if a binder which is not easily decomposed, such as afluororesin or a silicone resin, is used, the binder covers the surfacesof titanium dioxide particles and inhibits the exposure of titaniumdioxide to light and the contact of material to be decomposed withtitanium dioxide, thus reducing the photo-catalytic effect. Further theresin binder must be cured by heating. Even If titanium dioxide Is usedas a composite particle to enhance the desired function of titaniumdioxide, the above-mentioned problems arise.

DISCLOSURE OF THE INVENTION

Objects of the present invention are to provide a photo-catalyticcomposite particle comprising titanium dioxide particles or otherphoto-catalytic inorganic oxide particles which exhibits enhancedphoto-catalytic activity with high efficiency and practical use of whichis not restricted; a method for producing the composite particle; anorganic polymer composition comprising the composite particle; andapplications of the composite particle.

The inventors made intensive researches, and found that theabove-mentioned problems of the prior art can be overcome by a compositeparticle comprised of a larger particle and smaller particles which arephotocatalyst-containing fine particles having a specific averageparticle diameter as calculated from a BET surface area, especiallytitanium dioxide-silica fine composite particles or fine particlescontaining a Brφnsted acid salt, especially titanium dioxide fineparticles containing a Brφnsted acid salt on the surface thereof. Thepresent invention has been completed based on this finding.

Thus, in accordance with the present invention, there are provided thefollowing composite particle, method for producing the compositeparticle, organic polymer composition, and applications of the compositeparticle.

(1) A composite particle comprised of a larger particle and, supportedthereon, smaller particles wherein the smaller particles arephotocatalyst-containing fine particles having an average particlediameter in the range of 0.005 μm to 0.5 μm as calculated from a BETspecific surface area, and the larger particle has an average particlediameter in the range of 2 μm to 200 μm as measured by the laserdiffraction-scattering particle size measuring method.

Typical embodiments of the composite particle as mentioned above in (1)include those which are recited below in (2) through (12).

(2) The composite particle as mentioned above in (1), wherein thesmaller particles comprise titanium dioxide as a photocatalyst.

(3) The composite particle as mentioned above in (1), wherein thesmaller particles are composite particles comprising titanium dioxideand an inorganic compound exhibiting no photo-catalytic activity.

(4) The composite particle as mentioned above in (1), wherein theinorganic compound exhibiting no photo-catalytic activity is silica andthe content of silica in the smaller particles is at least 0.5% by massbut not larger than 50% by mass, based on the mass of the smallerparticles.

(5) The composite particle as mentioned above in-any one of (1) to (4),wherein the smaller particles contain a Brφnsted acid salt.

(6) The composite particle as mentioned above in (5), wherein thesmaller particles are titanium dioxide particles containing the Brφnstedacid salt on the surfaces of particles.

(7) The composite particle as mentined above in (6), wherein theBrφnsted acid salt is a condensed phosphate.

(8) The composite particle as mentioned above in any one of (5) to (7),wherein the smaller particles contain the Brφnsted acid salt in anamount In the range of 0.01% by mass to 50% by mass.

(9) The composite particle as mentioned above in any one of (2) to (8),wherein the titanium dioxide comprises a brookite crystalline phase.

(10) The composite particle as mentioned above in (1) to (9), whereinthe larger particle is a spherical resin particle having a melting pointof at least 150° C.

(11) The composite particle as mentioned above in any one of (1) to (9),wherein the larger particle is comprised of a hydroxide, oxide orcarbonate, which contains at least one kind of element selected from thegroup consisting of aluminum, magnesium, calcium and silicon.

(12) The composite particle as mentioned above in any one of (1) to(11), wherein the amount of smaller particles is in the range of 0.5% bymass to 40% by mass based on the mass of the larger particle.

(13) A method of producing a composite particle as mentioned above inany one of (1) to (12), comprising dry-mixing the smaller particles andthe larger particle by a ball mill, characterized in that the dry-mixingis carried out under conditions such that k value as defined by thefollowing equation (1) is in the range of 50 to 50,000,k=(wm/wp)×d×n×t   equation (1):where k is energy constant for dry-mixing,

wp is total mass (g) of particles to be dry-mixed,

wm us mass (g) of mixing media,

d is inner diameter (m) of ball mill,

n is number of rotation (rpm) of ball mill, and

t is time (min) for dry-mixing.

(14). A method of producing a composite particle as mentioned above inany one of (1) to (12), comprising mixing, pulverizing and stirring thesmaller particles and the larger particle by a powder-treating apparatusprovided with rotary blades, characterized in that the mixing,pulverizing and stirring are carried out under conditions such that k2value as defined by the following equation (2) is in the range of 250 to50,000,k2=n×t   equation (2):where n is number of rotation (rpm) of rotary blades, and

t is time (min) for mixing, pulverizing and stirring.

(15) A method of producing a composite particle as mentioned above inany one of (1) to (12), comprising mixing, pulverizing and stirring thesmaller particles and the larger particle by a shaking-typepowder-treating apparatus, characterized in that the mixing, pulverizingand stirring are carried out under conditions such that k3 value asdefined by the following equation (3) is in the range of 50 to 50,000,k3=n×t   equation (3):where n is number of shaking per minute, and

t is time (min) for mixing, pulverizing and stirring.

(16) A organic polymer composition comprising an organic polymer and acomposite particle as claimed in any one of claims 1 to 12, wherein theamount of the composite particle is in the range of 0.01% to 80% by massbased on the total mass of the organic polymer composition.

Typical embodiments of the organic polymer composition as mentionedabove in (16) include those which are recited below in (17) through(19).

(17) The organic polymer composition as mentioned above in (16) whereinthe organic polymer is at least one kind of resin selected from thegroup consisting of synthetic thermoplastic resins, syntheticthermosetting resins and natural resins.

(18) The organic polymer composition as mentioned above in (16) or (17)wherein the organic polymer composition is a compound.

(19) The organic polymer composition as mentioned above in (16) or (17)wherein the organic polymer composition is a master batch

(20) A shaped article made by shaping an organic polymer composition asmentioned above in any one of (16) to (19).

Typical applications of the composite particle as mentioned above in anyone of (1) through (12) include those which are recited below in (21)through (26).

(21) A coating composition comprising a composite particle as mentionedabove in any one of (1) to (12).

(22) A paint composition comprising a composite particle as mentionedabove in any one of (1) to (12).

(23) A structure comprising on a surface thereof a composite particle asmentioned above in any one of (1) to (12).

(24) A cosmetic composition comprising a composite particle as mentionedabove in any one of (1) to (12).

(25) A fiber comprising a composite particle as mentioned above in anyone of (1) to (12).

(26) A film comprising a composite particle as mentioned above in anyone of (1) to (12).

BEST MODE FOR CARRYING OUT THE INVENTION

The composite particle of the present invention is characterized asbeing comprised of a larger particle and, supported thereon, smallerparticles wherein the smaller particles are photocatalyst-containingfine particles having an average particle diameter in the range of 0.005μm to 0.5 μm as calculated from a BET specific surface area, and thelarger particle has an average particle diameter In the range of 2 μm to200 μm as measured by the laser diffraction-scattering particle sizemeasuring method.

The photocatalyst-containing fine particles are excited by ultravioletrays and visible light to give conduction electrons and positive holes.As specific examples of the photocatalyst-containing fine particles,there can be mentioned fine particles of titanium dioxide, tin oxide,zinc oxide, ferric oxide, tungsten trioxide, dibismuth trioxide andstrontium titanate. Of these, titanium dioxide is preferable because ofchemical stability.

Especially preferable smaller particles are composite particlescomprising titanium dioxide and an inorganic compound exhibiting nophoto-catalytic activity. As specific examples of the inorganic compoundexhibiting no photo-catalytic activity, there can be mentioned inorganiccompounds containing Mg, Si, Ca, Fe or Zr. Of the inorganic compounds,silica Is preferable.

The reason for which composite particles comprising titanium dioxide andan inorganic compound exhibiting no photo-catalytic activity, especiallytitanium-silica composite particles, are preferable as child particlesare as follows. Titanium dioxide ingredient in the composite particleshas photo-catalytic activity, and Mg, Si, Ca, Fe or Zr ingredientexhibits a strong binding performance via an oxygen atom for binding amother particle with child particles or binding child particle with aresin. Further, the inorganic compound exhibiting no photo-catalyticactivity does not decompose an organic polymer binder adjacent to theinorganic compound, and thus, the composite particles exhibit goodweather resistance. If the particular kinds of mother particle and childparticles are selected so that they are strongly bonded together,especially excellent composite particles are obtained. Thus, compositeparticles comprising titanium dioxide and an inorganic compoundexhibiting no photo-catalytic activity, especially titanium-silicacomposite particles, as child particles, give a composite particleexhibiting high photo-catalytic activity, and give a structure havinghigh durability, even when a conventional organic polymer binder isused.

Smaller particles containing a Brφnsted acid salt are also preferable.Titanium dioxide particles containing a Brφnsted acid salt on thesurfaces of particles are especially preferable because the Brφnstedacid salt on the particle surface has a function for strongly binding amother particle with child particles. In the case when titanium dioxideparticles containing a Brφnsted acid salt on the surfaces of particlesare used, a photo-catalytic activity can be manifested-even to a weaklight such as a ultraviolet rays of an intensity of, e.g., about 6μW/cm². By using as child particles titanium dioxide-silica compositeparticles and/or titanium dioxide fine particles containing a Brφnstedacid salt, a composite particle exhibiting high photo-catalytic activityand a structure having high durability are obtained, even when aconventional organic polymer binder is used.

The state of the Brφnsted acid salt on the surfaces of smaller particlesis not particularly limited, but preferably the Brφnsted acid saltconceals partly the surfaces of smaller particles and the covering ofBrφnsted acid salt may be of any fashion including, for example, islandsform and mask-melon form (i.e., network form).

When the titanium dioxide-silica composite fine particles or theBrφnsted acid salt-containing fine titanium dioxide particles arecombined as child particles with a mother particle having an adequateparticle size, a preferable composite particle is obtained. In the casewhen this composite particle is incorporated in a resin to form a fiberor a film or the composite particle is incorporated with a binder toform a coating on a surface of a base material, or the compositeparticle is incorporated in a structural member, the mother particle ofthe composite particle is capable of being partly exposed to light, thatis, titanium dioxide present on the surface of mother particle can bepartly exposed to light. Further, when an organic polymer is used as abinder, the surface of mother particle having no photo-catalyticactivity is partly directly contacted and connected with the binder, andtherefore, even when the organic polymer binder partly contacted withtitanium dioxide is oxidized or decomposed, the connection between theorganic polymer binder and the composite particle can be retained, andthe undesirable separation of the titanium dioxide-silica composite fineparticles or the Brφnsted acid salt-containing fine titanium dioxideparticles from the mother particle can prevented or minimized.Therefore, the above-mentioned composite particle of the presentinvention can give a durable structure exhibiting a photo-catalyticactivity for a long period of time. Such durable structure can beobtained without use of an expensive fluororesin or silicone resin whichis not easily decomposed.

The amount of smaller particles in the composite particle of the presentinvention is preferably in the range of 0.5% by mass to 40% by massbased on the mass of the larger particle. When the amount of smallerparticles is too small, a photo-catalytic activity of desired extentcannot be obtained. In contrast, when the amount of smaller particles istoo large, the proportion of mother particle exposed on the surface of astructure becomes too small, and thus the exposure of titanium dioxidepresent on the surface of mother particle is liable to be insufficient.

A preferable titanium dioxide-silica composite fine particle of thepresent invention is composite metal oxide particles (mixed crystalparticles) wherein titanium dioxide and silicon oxide exist in a mixedcrystal state as primary particle. The composite metal oxide ultrafinemixed crystal particles wherein titanium dioxide and silicon oxide existin a mixed crystal state as primary particles are prepared by a gaseousphase method or a liquid phase method. The preparation method is notparticularly limited. A preferable example of the preparation method isdescribed, for example, in WO01/56930. More specifically the compositemetal oxide ultrafine mixed crystal particles are prepared by a processwherein a mixed gas comprised of at least one compound selected fromtitanium chloride, titanium bromide and titanium iodide and at least onecompound selected from silicon chloride, silicon bromide and siliconiodide, and an oxidizing gas are separately pre-heated at a temperatureof at least 500° C., and then the pre-heated gases are allowed to reactwith each other.

In the case when a composite particle of the present invention is usedfor purposes other than the utilization of the photo-catalytic activityof titanium dioxide, a different metal oxide crystalline structurehaving a core/shell structure may be adopted. For example, there can beadopted a titanium dioxide-silica composite particle comprised ofprimary particles containing a mixed crystal state having atitanium-oxygen-silicon bond, which have a core predominantly comprisedof TiO₂ phase and a sheath predominantly comprised of SiO₂ phase. TheSiO₂ phase may be present In the sheath either in the form of a denselayer, or a islands, a group of islands or a network.

Preferable child particles in the composite particle of the presentinvention are not a simple mixture comprised of a titanium dioxidepowder and a silica powder, regardless of uses. Titanium dioxide in thetitanium dioxide-silica composite fine particle wherein titanium dioxideand silicon oxide exist in a mixed crystal state as primary particles,may be any of anatase, rutile and brookite crystalline phases. From aviewpoint of high photo-catalytic activity, anatase titanium dioxide andbrookite titanium dioxide are preferable. From a viewpoint ofultraviolet rays-screening, rutile titanium dioxide and anatase titaniumdioxide are preferable.

The smaller particles, i.e., child particles used in the presentinvention, have an average primary particle diameter in the range of0.005 μm to 0.5 μm (i.e., 5 nm to 500 nm), preferably 0.02 μm to 0.2 μmand more preferably 0.05 μm to 0.15 μm as calculated from a BET specificsurface area. The particle diameter as calculated from a BET specificsurface area is determined by converting the particles as sphereparticles and calculating the particle diameter according to thefollowing equation:D1=6/ρSwhere D1 is particle diameter as calculated from a BET specific surfacearea, ρ is density of particle, and S is specific surface area ofparticle

As the particle diameter of particles having a photo-catalytic activitydecreases, that is, the specific surface area of the particlesincreases, the photo-catalytic activity is enhanced. Therefore, theaverage primary particle diameter is up to 0.5 μm. If the averageprimary particle diameter is larger than 0.5 μm (500 nm), thephoto-catalytic activity is generally low. However, if the averageprimary particle diameter is smaller than 5 nm, a powder comprising thechild particles is bulky and difficult to handle and the productivity isliable to be drastically reduced.

The content of silica in the child particles is in the range of 0.5% bymass to 50% % by mass, preferably 1% by mass to 30% by mass, and morepreferably 1.5% by mass to 25% by mass. If the silica content is smallerthan 0.5% by mass, an organic structure containing the child particlestends to be subject to yellow change and its tenacity is liable to belowered, when it is irradiated with light. This would be due to the factthat probability of contact between titanium dioxide and an organicmaterial increases. In contrast, if the silica content in the childparticles is larger than 50% by mass, the photo-catalytic activity oftitanium dioxide tends to be manifested to a reduced extent. This wouldbe due to the fact that the relative amount of titanium dioxide isreduced.

Now child particles containing a Brφnsted acid salt will be described.

The Brφnsted acid salt used is not particularly limited, and, asspecific examples thereof, there can be mentioned phosphates, condensedphosphates, borates, sulfates, condensed sulfates and carboxylates. Ofthese, preferable are salts capable of forming a compound insoluble inwater or only slightly soluble in water together with the metalconstituting the mother particle. Of these, polybasic acid salts such ascondensed phosphates, borates, condensed sulfates and polycarboxylatesare preferable. Condensed phosphates are especially preferable.

The condensed phosphates include, for example, pyrophosphates,tripolyphosphates, tetrapolyphosphates, metaphosphates andultraphosphates. Of these, pyrophosphates and tripolyphosphates arepreferable.

The Brφnsted acid salt may be present either alone or as a combinationof two or more thereof.

The content of Brφnsted acid salt in the smaller particles is preferablyin the range of 0.01% by mass to 50% by mass, If the content of Brφnstedacid salt is too small, a photo-catalytic activity of a desired extentcannot be manifested upon irradiation with weak light, and thedurability of a photo-catalytic structure is liable to be reduced. Incontrast, if the content of Brφnsted acid salt is too large, therelative area of titanium dioxide or other material having aphoto-catalytic activity, exposed on the surfaces of particles, isreduced and the photo-catalytic performance tends to be lowered.

The child particles preferably have a BET specific surf ace area in therange of 5 to 300 m²/g. The average particle diameter as calculated fromthis BET specific surface area is in the range of 0.005 μm to 0.3 μm.The BET specific surface area is more preferably in the range of 30 to250 m²/g, especially preferably 50 to 200 m²/g. If the BET specificsurface area is smaller than 10 m²/g, the photo-catalytic activity tendsto be small. In contrast, a composite particle having child particleshaving a BET surface area of at least 300 m²/g is difficult to producewith good productivity and thus is of poor practicality.

Titanium oxide may have any of anatase, rutile and brookite crystallinephases. Anatase and brookite crystalline phases are preferable. Brookitecrystalline phase is especially preferable. Titanium oxide may have twoor more of the three crystalline phases. In some cases, the activity oftitanium dioxide having at least two crystalline phases is larger thanthose of the sum of respective single crystalline phases.

The process for preparing the titanium dioxide is not particularlylimited, but, the titanium dioxide is generally prepared by a vaporphase process using a TiCl₄ material, or a liquid phase process using anaqueous TiCl₄ solution or an aqueous titanyl sulfate solution. Theliquid phase process using an aqueous TiCl₄ solution includes, forexample, a process as described in JP-A H11-43327 wherein titaniumtetrachloride is incorporated in hot water maintained at a temperatureof 75 to 100° C. and then hydrolysis is effected at a temperature of 75°C. to the boiling point of the solution to prepare an aqueous sol ofbrookite titanium dioxide.

To support titanium dioxide on the surface of mother particle with anenhanced efficiency, titanium dioxide prepared by the liquid phaseprocess is preferably used. More preferably titanium dioxide slurry asobtained in the liquid phase process is used as it is, namely, withoutdrying into a titanium oxide powder. This is because titanium dioxideundesirably agglomerates in the step of preparing a powder from theslurry as-obtained in the liquid phase process. Thus an additional stepof pulverizing the agglomerates by using an air-stream pulverizer suchas a micronizer or jet mill, a roller mill or a pulperizer is needed.

The aqueous titanium dioxide slurry used preferably has a titaniumdioxide content in the range of 0.1% to 10% by mass, more preferably0.5% to 5% by mass. When the titanium dioxide content in slurry islarger than 10% by mass, titanium dioxide tends to be agglomerated inthe succeeding mixing step. In contrast, when the titanium dioxidecontent in slurry is smaller than 0.5% by mass, the productivity islowered.

The titanium dioxide in the aqueous slurry preferably has a pH value inthe range of 3 to 5. When the pH value of titanium dioxide is lower than3, titanium dioxide tends to be agglomerated by local neutralization orexothermic heat at mixing in the succeeding reaction step. When thetitanium dioxide has a pH value higher than 5, the agglomerationundesirably proceeds. If desired, an aqueous titanium dioxide slurry asobtained by a vapor phase process or a liquid phase process may betreated by electrodialysis or with ion-exchange resin to adjust the pHvalue.

The method of preparing composite particles of titanium dioxide with aBrφnsted acid salt is not particularly limited, but preferably theBrφnsted acid salt is used as an aqueous solution. If the Brφnsted acidsalt is incorporated as a powder in an aqueous slurry of titaniumdioxide, the titanium dioxide occasionally tends to exhibit a lowabsorbance of visible light.

If a Brφnsted acid salt used has a poor solubility in water, aqueoussolutions of a plurality of raw materials capable of forming a compoundhaving a poor solubility in water are preferably used. For example, whencomposite particles of titanium dioxide with calcium pyrophosphate areprepared, it is preferable to use in combination an aqueous solution ofsodium pyrophosphate and an aqueous solution of calcium chloride.

The aqueous solution of a Brφnsted acid salt preferably has aconcentration of not higher than 40% by mass, more preferably not higherthan 20% by mass. When the concentration of a Brφnsted acid salt ishigher than 40% by mass, titanium dioxide tends to be locallyagglomerated in the succeeding mixing step.

The amount of a Brφnsted acid salt used is in the range of 0.01% to 50%by mass based on the mass of the smaller particles. Usually the amountof a Brφnsted acid salt used is in the range of 0.01% to 100% by mass,preferably 0.1% to 50% by mass, based on the mass of the titaniumdioxide. When the amount of a Brφnsted acid salt Is smaller than 0.01%by mass, its reactivity with titanium dioxide is insufficient. Incontrast, the use of a Brφnsted acid salt in an amount of larger than50% by mass is not advantageous from cost considerations, andoccasionally leads to agglomeration of titanium dioxide particles.

For the preparation of a composite particle, an aqueous titanium dioxideslurry is mixed with the aqueous solution of a Brφnsted acid salt.

The mixing is preferably carried out at a pH value in the range of 4 to10, more preferably 5 to 9. If the pH value is lower than 4, thereactivity of titanium dioxide with a Brφnsted acid salt isinsufficient. In contrast, if the pH value is higher than 10, titaniumdioxide tends to be undesirably agglomerated at mixing.

The adjustment of pH value at mixing can be carried out when an aqueoustitanium dioxide slurry is mixed with the an aqueous solution of aBrφnsted acid salt, or the pH value of the aqueous Brφnsted acid saltsolution can be previously adjusted so that a mixed solution thereofhaving a desired pH value is obtained when the aqueous Brφnsted acidsalt solution is mixed with an aqueous titanium dioxide slurry. Theadjustment of pH value can be effected by adding an aqueous solution ofa mineral acid such as hydrochloric acid or sulfuric acid, or a basesuch as sodium hydroxide or ammonia. It should be noted, however, thatthe amount of pH adjuster is minimized as soon as possible or the pHadjuster is used at a concentration as low as possible so as to avoid orminimize undesirable local agglomeration of titanium dioxide rawmaterial and produced composite particles at mixing sites.

As the method of mixing an aqueous titanium dioxide slurry with anaqueous Brφnsted acid salt solution, there can be adopted a method ofcontinuously adding an aqueous Brφnsted acid salt solution to an aqueoustitanium dioxide slurry, and a method of simultaneously adding anaqueous Brφnsted acid salt solution and an aqueous titanium dioxideslurry into a reacting vessel.

A mixed liquid of an aqueous Brφnsted acid salt solution with an aqueoustitanium dioxide slurry preferably has a concentration of titaniumdioxide not larger than 5% by mass, more preferably not larger than 3%by mass. When a mixed liquid having a concentration of titanium dioxideexceeding 5% by mass is prepared, titanium dioxide tends to beagglomerated at mixing.

The temperature at which a Brφnsted acid salt reacts with titaniumdioxide is preferably not higher than 50° C., more preferably not higherthan 30° C. At a reaction temperature higher than 50° C., fine particlesare liable to be agglomerated together in a reaction vessel.

The aqueous slurry obtained by the reaction of a Brφnsted acid salt withtitanium dioxide can be subjected to a salt-removal treatment. By theremoval of excessive salt, the dispersibility of particles in theaqueous slurry is enhanced. The method of salt-removal includes, forexample, a method using an ion-exchange resin, a method usingelectrodialysis, a method using an ultrafiltration membrane and a methodusing a rotary filter press which is available, for example, fromKotobuki Giken K.K.

In general, if a compound having no photo-catalytic activity is presenton the surface of titanium dioxide particle, the photo-catalyticactivity of titanium dioxide is reduced. It is surprising, however, thatsmaller particles comprised of titanium dioxide having, supported on thesurfaces thereof, a compound having no photo-catalytic activityaccording to the present invention, exhibit enhanced photo-catalyticactivity as compared with smaller particles comprised of untreatedtitanium dioxide. This beneficial effect is obtained in the case whenthe whole process of the above-mentioned surface treatment of titaniumoxide particle Is carried out under conditions such that undesirableagglomeration of titanium dioxide particles and the resulting compositeparticles can be avoided or minimized. Especially when the titaniumdioxide particles are partially surface-treated with a polybasic acidsalt, the above-mentioned beneficial effect is markedly manifested. Thereason for which is not clear, but it is presumed that a plurality ofelectron-absorbing carboxyl groups or sulfonyl groups exhibit mutualfunction prefentially to specific titanium atoms on the particlesurface, and consequently electrons produced in the titanium dioxideparticles upon irradiation with light are subject to charge transfer,with the result of enhancement in the photo-catalytic activity.

It is also presumed that energy level of a specific titanium-containingcomposite oxide is newly formed on the surface of titanium dioxideparticle, and some of the composite oxide can possess a band gapresponsible to visible light rays.

It is generally believed that, in the case when titanium dioxideparticles are surface-treated with a compound having no photo-catalyticactivity, the photo-catalytic activity of titanium dioxide isdeteriorated. This is not always true. Further, it is to be noted that achemical group having introduced onto the titanium oxide surface by thesurface treatment with the compound having no photo-catalytic activityhas an end atomic group moiety exhibiting no photo-catalytic activity,and therefore, when the surface-treated titanium dioxide particles areincorporated with an organic material, the end atomic group moietysterically prevents the contact of the organic material with titaniumdioxide, and therefore, a structure composed of the surface-treatedtitanium dioxide particles and the organic material has enhanceddurability. More specifically it is to be noted that the contact of thesurface-treated titanium dioxide particles with a solid organic materialcan be sterically hindered, but, a material to be decomposed by thestructure composed of the surface-treated titanium dioxide particles andthe organic material is gaseous or liquid and has a high mobility, andtherefore, the contact of titanium dioxide with the material to bedecomposed can be easily obtained. This leads to the above-mentionedcompatibility of high photo-catalytic activity with enhanced durability.

That is, by the surface-treating process of titanium dioxide whereingood dispersion of titanium dioxide particles is kept withoutagglomeration, a desired mutual action can be obtained between thepolybasic acid salt and specific titanium atoms on the particle surface,with the result of the above-mentioned compatibility of photo-catalyticactivity higher than that of untreated titanium dioxide particles, withenhanced durability or weather resistance.

The child particles comprised of titanium dioxide particles and,supported thereon, a Brφnsted acid salt can be taken as a powderprepared by drying the particles obtained by the above-mentioned surfacetreating process. The powder is liable to be agglomerated, andtherefore, is usually pulverized by an airflow pulverizer such as a jetmill or a micronizer, or a roller mill or a pulperizer.

The mother particle has an average particle diameter in the range of 2to 200 μm, preferably 3 to 100 μm, and more preferably 3 to 80 μm, asmeasured by the laser diffraction-scattering particle size measuringmethod. When the mother particle has this size, it is advantageous tosupport the particle on the surface of a base material or structure. Ifthe mother particle has a smaller size, it is difficult to handle andsupport the particle on the surface thereof. In contrast, if the motherparticle has a larger size, the surface of base material or structurehaving the particle supported thereon is rough and not smooth.

By the term “particle diameters” of mother particle (larger particle)and child particles (smaller particles) in the composite particle of thepresent invention, as used in this specification, we mean not theparticle diameters of mother particle and child particles as measuredbefore the preparation of the composite particle, but, the particlediameters of mother particle and child particles as measured after thepreparation of the composite particle. Therefore, the mother particle asmeasured before it is pulverized and mixed for processing into thecomposite particle may have a size larger than a diameter of 200 μm. Thechild particles as measured before the preparation of the compositeparticle may also have a size larger than a diameter of 0.5 μm, butusually the child particles as measured after the preparation ofcomposite particle have approximately the same size as that as measuredbefore the preparation of composite particle.

The mother particle may be a spherical resin particle. Sphericalparticles are beneficial in that, at the step of preparing compositeparticles including the step of treating, for example, by a ball mill,undesirable packing of particles to an excessive extent and stickingoccurring among particles to be made Into composite particles or betweensuch particles and mixing media such as balls can be easily avoided.

The mother particle preferably has a melting point of at least 150° C.In the case when a composite particle made from the mother particlehaving such a high melting point is blended and kneaded together withanother resin to form a molding at a high temperature, the motherparticle has good shape retention and therefore the performance of thechild particles of the composite particle in the molding can bemanifested to a sufficient extent.

The mother particle can be comprised of a hydroxide, oxide or carbonate,which contains at least one kind of element selected from the groupconsisting of aluminum, magnesium, calcium and silicon. Preferableexamples of the mother particle are particles of a hydroxide or oxide ofaluminum, magnesium or calcium, particles of a carbonate of calcium, andparticles of silica. As specific examples of the mother particle, therecan be mentioned particles of aluminum hydroxide, magnesium hydroxide,calcium hydroxide, aluminum oxide, magnesium oxide, calcium oxide,calcium carbonate and silica. The mother particle may be a composite oftwo or more of these particles.

The shape of mother particle and the method of preparing mother particleare not particularly limited, provided that the mother particle has theabove-specified particle diameter.

When the above-mentioned mother particle and the child particlecontaining, for example, silica or a Brφnsted acid salt are subjected tomixing, pulverizing and stirring under specific conditions, the motherparticle can be strongly bonded to silica or a Brφnsted acid salt of thechild particles. That is, in the case when the mother particle and thechild particles are dry-mixed together by a ball mill under conditionssuch that k value as defined by the equation (1) below is in the rangeof 50 to 50,000; or are subjected to mixing, pulverizing and stirring bya powder-treating apparatus provided with rotary blades under conditionssuch that k2 value as defined by the equation (2) below is in the rangeof 250 to 50,000; or are subjected to mixing, pulverizing and stirringby a shaking-type powder-treating apparatus under conditions such thatk3 value as defined by the equation (3) below is in the range of 50 to50,000; a composite particle wherein the mother particle is stronglybonded to the child particles can be obtained.

When the mother particle (larger particle) and the child particles(smaller particles) are made into a composite particle, the childparticles and the mother particle or a precursor particle for the motherparticle are mixed, pulverized and stirred with a predetermined energyconstant. A mixing medium for mixing, pulverizing and stirring givesimpact energy, frictional energy and shearing energy to the particleswhereby the surfaces of particles are activated to form a compositeparticle.

The means for mixing, pulverizing and stirring for forming a compositeparticle includes various mixing and pulverizing means, and mechanicalmelt-processing means. For example, a rolling ball mill, a high-speedrotary pulverizer, a mixing medium-stirring mill, a high-speed airflowimpact pulverizer, and a surface-melting apparatus can be used.Operating factors for giving adequate impact energy, frictional energyand shearing energy to particulate materials include, for example,number of revolution and residence time for a high-speed rotarypulverizer; rate of stirring, mass of mixing media and stirring time fora mixing medium-stirring mill; and pressure of carrier gas and residencetime for a high-speed airflow impact pulverizer.

A ball mill, which is a most popular mixing and pulverizing apparatus,is preferable for forming a composite particle because a constant energycan be given to particles by appropriately choosing operating factors.Energy constant k can be a measure for the energy consumed for theformation of a composite particle. Energy constant k as defined by theequation (2) below has been proposed as a measure for evaluating themixing and pulverizing effect of a rolling ball mill (L. D. Hart and L.K. Hadson, The American Ceramic Society Bulletin, 43, No. 1 (1964).k=(wm/wp)×d×n×t   Equation (1):where k is energy constant,

wp is total mass (g) of particles to be mixed,

wm is mass (g) of mixing media,

d is Inner diameter (m) of ball mill,

n is number of rotation (rpm) of ball mill, and

t is time (min) for mixing.

In the case when mixing, pulverizing and stirring are carried out by apowder-treating apparatus provided with rotary blades, the energyconstant is expressed by a k2 value as defined by the following equation(2).k2=n×t   Equation (2):where n is number of rotation (rpm) of rotary blades, and

t is time (min) for mixing, pulverizing and stirring.

In the case when mixing, pulverizing and stirring are carried out by ashaking-type powder-treating apparatus, the energy constant is expressedby a k3 value as defined by the following equation (3).k3=n×t   Equation (3):where n is number of shaking per minute, and

t is time (min) for mixing.

In any cases, as the energy constant is larger, the energies of impact,friction and shear are larger and the bonding force between the motherparticle and the child particles is enhanced.

In the process for preparing a composite particle of the presentinvention, when an apparatus giving energy to particles by rolling apulverizing and mixing medium, such as a ball mill, is used, the energyconstant k for mixing, pulverizing and stirring the mother particle andthe child particles, as defined by the equation (1) is in the range of50 to 50,000, preferably 750 to 20,000, and more preferably 1,000 to15,000.

When an apparatus giving energy to particles by rotary blades is used,the energy constant k2 as defined by the equation (2) is in the range of250 to 50,000, preferably 500 to 20,000, and more preferably 700 to15,000.

When an apparatus giving energy to particles by shaking of a medium formixing and pulverization is used, the energy constant k3 as defined bythe equation (3) is in the range of 50 to 50,000, preferably 250 to20,000, and more preferably 700 to 15,000.

If the energy constant is smaller than the above-specified lower limits,the surfaces of particles cannot be activated to the desired extent andthe bonding of particles are insufficient. In contrast, if the energyconstant is larger than the respective upper limits, pulverizationproceeds to a great extent and the particles become very fine, and theparticle surfaces are greatly activated, with the result that bonding ofparticles occurs to an undue extent and coarse particles are formed.Further, if the energy constant is too large, the activated particlestend to stick to a pulverizing medium and to the inner wall of a vessel.

The apparatus used for the formation of the composite particle is notparticularly limited, and includes, for example, a conventional ballmill, a powder-treating apparatus provided with rotary blades such as asuper-mixer available from K.K. Kawata, a shaking-type powder treatingapparatus such as a paint-shaker available from Asada Tekkou K.K.,Hybridization System available from Nara Kikai Mfg. Co., Mechanofusion™available from Hosokawa Micron K.K., a medium-flow dryer, an airflowimpact apparatus and a surface-melting apparatus.

Means for forming the composite particle, other than the above-mentionedrolling ball mill type, rotary blade type and shaking type apparatuses,can also be used. In this case the energy required for formation of thecomposite particle should be adequately controlled so that the power perunit mass of particulate materials is approximately the same as thosecorresponding to the magnitude of energy constant k in the case when aball mill is used.

In the case when smaller particles in the form of slurry comprised oftitanium dioxide particles and, supported on the surfaces thereof, aBrφnsted acid salt are combined with a larger particle to form acomposite particle, the larger particle can be incorporated in theslurry of smaller particles, and then the mixed slurry is placed in andtreated by a medium-flow drying apparatus. By adding the mixed slurry ina ceramic medium in a flow state, the shearing force of the media atmixing and the agglomerating force at drying apply whereby the largerparticle and the smaller particles are firmly bonded together.

The proportion of the smaller particles to the larger particle placed inan apparatus for forming the composite particle is such that the amountof smaller particles is in the range of 0.5% by mass to 40% by mass ofthe larger particle.

The composite particle of the present invention can be used in fieldssimilar to those of conventional titanium dioxide. For example, thecomposite particle is used for resin articles, rubber articles, paper,cosmetics, paints, printing inks, ceramic articles, dye sensitizingsolar batteries, and photo-catalysts.

The composite particle of the present invention can be used incombination with an organic polymer. The organic polymer includes, forexample, synthetic thermoplastic resins, synthetic thermosetting resinsand natural resins. As specific examples of the organic high polymer,there can be mentioned polyolefins such as polyethylene, polypropyleneand polystyrene; polyamides such as nylon 6, nylon 66 and aramide;polyesters such as polyethylene terephthalate and unsaturatedpolyesters; polyvinyl chloride, polyvinylidene chloride, polyethyleneoxide, polyethylene glycol, silicone resin, polyvinyl alcohol, vinylacetal resin, polyacetate, ABS resin, epoxy resin, vinyl acetate resin,cellulose and rayon and other cellulose derivatives, polyurethane,polycarbonate, urea resin, fluororesin, polyvinylidene fluoride,phenolic resin, celluloid, chitin, starch sheet, acrylic resin, melamineresin and alkyd resin. These organic polymers may be used either aloneor as a combination of at least two thereof.

The organic polymer composition comprising the composite particle of thepresent invention can be used for example, as a coating or paintcomposition, a compound (powder-containing resin composition), and amaster batch containing the composite particle at a high concentrationfor use, for example, in molding. Additives such as an antioxidant, anantistatic agent and a fatty acid metal salt can be incorporated in theorganic polymer composition.

The amount of the composite particle of the present invention ispreferably in the range of 0.01% to 80% by mass, more preferably 0.01%to 60% by mass, especially preferably 1% to 50% by mass and mostpreferably 1% to 40% by mass, based on the total mass of the organicpolymer composition.

By shaping the organic polymer composition, a shaped article having anultraviolet rays-screening performance can be obtained. Such shapedarticle includes, for example, fiber, film and plastic moldings.

The fiber includes, for example, polyolefin fiber, polyamide fiber,polyester fiber, acrylic fiber and rayon. These fibers can be made intovarious textile articles having a photo-catalytic activity. As specificexamples of the textile article, there can be mentioned clothes such astowel, dish cloth, hand-wiping cloth, glasses-wiping cloth andhandkerchief; bedding clothes and other clothes such as pajamas, diaper,bed sheet, toilet seat cover, blanket and futon (quilt); under wears andhoses; sanitary and hospital clothes such as mask, white garment, nursecap, curtain and bed sheet; sports wear and other sports goods such assupporter, training wears and jersey clothes; automobile clothes such asautomobile seat, seat cover, automobile ceiling and automobile floor;home clothes such as carpet, curtain, mat, decorative hanging cloth, andchair cloth and sofa cloth; and clothing such as sweater. Further, thefiber can be made into paper goods such as wall paper or cloth andsliding door paper or cloth.

As specific examples of the film, there can be mentioned waste bag film,food packing film, wrapping film, shrink film for PET bottle, andcosmetic film or cosmetic board.

As specific examples of the molding, there can be mentioned wash standunit, bath unit, plastic part of kitchen unit, plastic part of handrail, television set, personal computer, indoor air-conditioner, copyingmachine, washing machine, dehumidifier, telephone set, electrical-potand plastic body of electrical cleaner, plastic cover of lightingappliance, plastic hanger, plastic dress container, plastic waste box,and automobile dashboard.

In a shaped article made from the organic polymer composition comprisingthe composite particle of the present invention, the mother particle ispartially exposed on the surface of shaped article. In the case when theorganic polymer composition is shaped into fiber or film, the fiberdiameter and the film thickness are not particularly limited. However,the fiber diameter and the film thickness are preferably in the range of2 to 200 times, more preferably 5 to 100 times of the average particlediameter of the mother particle.

The composite particle of the present invention can be dispersed inwater or an organic solvent, and if desired, a binder is added toprepare a coating composition. The binder used is not particularlylimited, and may be either an organic binder or inorganic binder.

As specific examples of the organic binder, there can be mentionedpolyvinyl alcohol, melamine resin, urethane resin, celluloid, chitin,starch sheet, polyacrylamide, polyester such as unsaturated polyester,polyvinyl chloride, polyvinylidene chloride, polyethylene oxide,polyethylene glycol, silicone resin, vinyl acetal resin, epoxy resin,vinyl acetate resin, polyurethane, urea resin, fluororesin,polyvinylidene fluoride and phenolic resin. As specific examples of theinorganic binder, there can be mentioned zirconium compounds such aszirconium oxychloride, zirconium hydroxychloride, zirconium nitrate,zirconium sulfate, zirconium acetate, zirconium ammonium carbonate andzirconium propionate; silicon compounds such as alkoxysilanes andsilicates; and metal alkoxides such as aluminum alkoxides and titaniumalkoxides.

The amount of binder in the coating composition is preferably in therange of 0.01% to 20% by mass, more preferably 1% to 10% by mass basedon the mass of the coating composition. If the amount of binder issmaller than 0.01% by mass, a resulting coating does not exhibit asufficient adhesion. In contrast, if the amount of binder exceeds 20% bymass, the coating composition is undesirably thickened and notadvantageous from cost consideration.

The composite particle of the present invention can be provided oradhered onto the surface of a structure. The structure used is notparticularly limited, and includes, for example, those comprised of aninorganic material such as metal, concrete, glass or pottery; or anorganic material such as paper, plastic material, wood or leather; or acombination of two or more thereof. As specific examples of thestructure, there can be mentioned building materials, machines,vehicles, glass articles, electrical appliances, agricultural materials,electronic parts and instruments, tools, tableware, bathroom fittingsand accessories, toilet fittings and requisites, furniture, clothes,fabrics, fibers, leather articles, paper products, sports goods, futon(quilt), vessels and containers, glasses, sign-boards, piping, fitment,sanitary materials, automobile parts, outdoor goods such as tent,stockings, hosiery, gloves and masks. The structure further includesenvironmental cleaning or environmental damage-preventing equipments andinstruments, which are used for a remedy for sick houses, decompositionof harmful organic chlorine-containing compounds such aspolychlorobiphenyl (PCB) and dioxin present in water, air or soil, anddecomposition of residual pesticide present in water or soil andenvironmental hormone.

As examples of the light source for emission for developing withenhanced efficiency the photo-catalytic-activity or hydrophilic propertyof the structure comprising the composite particle on a surface thereof,there can be mentioned sun, fluorescent lighting, incandescent lamp,mercury lamp, xenon lamp, halogen lamp, mercury xenon lamp, metal halidelamp, light emitting diode, laser and burning flame of organic material.The fluorescent lighting includes, for example, cool white fluorescentlamp, white daylight fluorescent lamp, daylight fluorescent lamp, warmwhite fluorescent lamp, incandescent lamp-light fluorescent lamp andblack light lamp.

The method of preparing the structure comprising the composite particleon the surface thereof is not particularly limited, and includes, forexample, a method of directly coating a structure with theabove-mentioned organic polymer composition or the above-mentionedcoating composition, or a method of coating a structure having a coatingon the surface thereof with the above-mentioned organic polymercomposition or the above-mentioned coating composition. In the case whena structure is coated with the coating composition to form a filmycoating, it is possible that a composite particle Is partially exposedon the surface of film. In this case, the thickness of film ispreferably in the range of 2 to 200 times, more preferably 5 to 100times of the average particle diameter of mother particle.

The coated structure may be further coated with another coatingcomposition. In this case, it is preferable that the film formed bycoating does not cover the area in which the composite particle isexposed, or a material to be decomposed by the photo-catalytic activityis capable of permeating through the film formed by coating.

The composite particle of the present invention can be used incosmetics. A composite particle comprised of a mother particle and childparticles which are titanium-silica composite particles is especiallypreferable for use in cosmetics. The cosmetics containing this compositeparticle are advantageous over those which contain only the childparticles, i.e., titanium-silica composite particles. The cosmeticscontaining this composite particle smoothes the skin when applied to theskin. This advantage is more marked in the case when the mother particleis comprised of a spherical nylon particle. That is, the compositeparticle comprising a spherical nylon mother particle and, supportedthereon, titanium dioxide-silica composite particles as child particlesexhibits good smoothness and feeling when applied to the skin, and hasgood ultraviolet rays-screening performance.

Various additives can be incorporated in the cosmetics. The additivesinclude those which are conventionally used, and, as examples thereof,there can be mentioned oils, whitening agents, humectants, anti-agingagents, emollients, extracts and essences, anti-inflammatory agents,antioxidants, surface active agents, chelating agents, anti-fungusagents, antiseptics, amino acids, saccharides, organic acids, alcohols,esters, oils and fats, hydrocarbons, ultraviolet ray-absorbers andinorganic powders.

As specific examples of the additives, there can be mentioned solventssuch as ethanol, isopropanol, butyl alcohol and benzylalcohol;polyhydric alcohols such as glycerine, propylene glycol, sorbit,polyethylene glycol, dipropylene glycol, 1,3-butylene glycol and1,2-pentanediol; saccharides such as sorbitol; disaccharides such astrehalose; humectants such as hyaluronic acid and water-solublecollagen; hydrated squalane, vegitable oils such as olive oil andSimmondsia chinensis oil; emollients such as aeramide; stabilizedascorbic acid such as magnesium ascorbate phosphate and ascorbic acidglucoside; whitening agents such as arbutin, kojic acid, ellagic acid,rucinol and camomille essence; anti-inflammatory agents such asallantoin, glycylrhetinic acid and its salts; nonionic surface activeagents such as monostearic acid glyceride, polyoxyethylene (POE)sorbitan fatty acid esters, sorbitan fatty acid ester, polyoxyethylene(POE) alkyl ether, POE-POP block polymer and POE hardened castor oilester; anionic surface active agents such as fatty acid soaps and sodiumalkylsulafates; hydrocarbons such as squalane, fluid paraffin, paraffin,isoparaffin, vaseline and α-olefin oligomer; oils and fats such asalmond oil, cocoa butter, macadamia nut oil, avocado oil, castor oil,sunflower oil, evening primrose oil, safflower oil, rape seed oil, horseoil, tallow and synthetic triglyceride; waxes such as beeswax, lanolinand Simmondsia chinensis oil; fatty acids such as lauric acid, stearicacid, oleic acid, isosteario acid, myristic acid, palmitic acid, behenicacid, glycolic acid and tartaric acid; higher alcohols such as cetanol,stearyl alcohol, behenyl alcohol and octyldodecyl alcohol; syntheticesters such as glycerine triester and pentaerythrithol tetraester;silicone oils such as dimethyl polysiloxane and methylphenylpolysiloxane; chelating agents such as ethylenediaminetetraacetic acid(EDTA), gluconic acid, phytic acid and sodium polyphosphate; antisepticssuch as p-hydroxybenzoic acid esters, sorbic acid,isopropylmethyl-phenol, aresol, benzoic acid, ethyl benzoate,chlorostearyldimethylbenzyl ammonium, hinokitiol, furfural and sodiumpyrithioate; bactericides; antioxidants such as vitamin-E,dibutylhydroxytoluene, sodium hydrogensulfite and butylhydroxyanisole;buffering agents such as citric acid, sodium citrate, lactic acid andsodium lactate; amiono acids such as glycine and alanine; esters such asbutyl myristate, ethyl oleate and ethyl stearate; perfumes; pigments;animal extracts and vegetable extracts; vitamins such as vitamin A,vitamin B and vitamin C, and derivatives thereof; ultraviolet absorberssuch as p-aminobenzoic acid, octyl p-dimethylaminobenzoate, ethylp-aminobenzoate, phenyl salicylate, benzyl cinnamate, octylmethoxycinnamate, cinoxate, ethyl urocanate, hydroxymethoxybenzophenoneand dihydroxybenzophenone; inorganic powders such as mica, talc,kaoline, calcium carbonate, silicic anhydride, aluminum oxide, magnesiumcarbonate, barium sulfate, cerium oxide, red iron oxide, chromium oxide,ultramarine, black iron oxide and yellow iron oxide; and resin powderssuch as nylon powder and polymethyl methacrylate powder.

The procedures and conditions for preparation of the cosmetics may bethe same as those which are conventionally adopted in cosmetic industryexcept for the procedures and conditions for preparation of thecomposite particle of the present invention.

EXAMPLES

The invention will be described by the following examples that by nomeans limit the scope of the invention.

The methods of evaluation adopted in the following examples andcomparative examples are as follows.

(1) Photo-Catalytic Performance of Film

20 parts by mass of a composite particle of the present invention, 2parts by mass of zinc stearate (“Zinc stearate S” available from NOFCorporation) and 78 parts by mass of low density polyethylene (“J-REX™JH607C, available from Japan Polyolefins Corporation) were melted andkneaded together by a twin screw extruder (KZW15-30MG, available fromTechnovel Corporation) at 140° C. for a residence time of about 3minutes to prepare a pellet. The pellet was comprised of a low densitypolyethylene compound containing 20% of the composite particle, and eachpellet had a columnar shape having a diameter of 2 to 3 mm and a lengthof 3 to 5 mm, and a mass of 0.01 to 0.02 g.

4 kg of the above-mentioned composite particle-containing low densitypolyethylene compound was mixed together with 16 kg of low densitypolyethylene (“J-REX™ JH607C, available from Japan PolyolefinsCorporation) by a V-type blender (“RKI-40” available from Ikemoto RikaKogyo K.K.) for 10 minutes to prepare a mixed pellet.

The mixed pellet was melt-extruded by a twin screw kneading extruderequipped with a 200 mm T-die (KZW15-30MG, available from TechnovelCorporation) at a die temperature of 250° C. to make a film with athickness of 80 μm.

A test ink was dropped on the film so that the ink was spread into acircle having a diameter of about 2 cm to prepare a specimen forcolor-fading test. The test ink was a solution of 1 g of an ink forcolor printer (BJI201M-Magenta, available from Canon Inc.) in 99 g ofethanol.

The color-fading test specimen was placed 5 cm apart from a glasswindow. The specimen was irradiated with sunlight through the window,and color-fading was observed by the naked eye after accumulated threedays of fine weather elapsed.

(2) Hydrogen Sulfide Deodorizing Test

A specimen in an amount such that the total area-of photo-catalyticsurface was 400 cm² was placed in a 5 liter “Tedlar™ bag (AAK-5available from GL Sciences Inc.). Then 5 liters of dry air containing 60ppm by volume of hydrogen sulfide was blown into the bag at least onetime, and thereafter, 5 liters of dry air containing 60 ppm by volume ofhydrogen sulfide was blown into the bag whereby the inner gas wasthoroughly substituted. The dry air containing 60 ppm by volume ofhydrogen sulfide was prepared by permeator (PD-1B, available from GastecCorporation) using a commercially available compressed air.

The initial concentration of hydrogen sulfide C_(0T) (ppm by volume) wasmeasured by an indicator tube (No. 4LL, available form GastecCorporation). The specimen was irradiated with ultraviolet rays throughthe bag wall so that ultraviolet rays having an intensity of 0.5 mW/cm²at 365 nm were incident on the photo-catalytic surface. When 4 hourselapsed from the commencement of irradiation, the concentration ofhydrogen sulfide C_(1T) (ppm by volume) within the bag was measured. Fora control test, a similar test was conducted wherein thespecimen-containing bag was allowed to stand for 4 hours in the darkplace. The initial concentration of hydrogen sulfide and theconcentration of hydrogen sulfide as measured after 4 hours standingwere C_(0S) (ppm by volume) and C_(1B) (ppm by volume), respectively.

As a light source, black light lamp (FL20S-BL-B, available from NationalK.K.) was used. The intensity of light at 365 nm was measured by anultraviolet light quantity integrating meter (UIT-150 available fromUshio Inc.). In the case when a white daylight fluorescent lamp was usedas a light source, High White FL20SS-N/18-B available from Hitachi GELighting Co. was used. The intensity of light at 365 nm was measured byUVA-365 available from ATEX CORPORATION was used. By this measuringapparatus, a weak light intensity at 365 nm could be measured. Morespecifically the light irradiation test was conducted so thatultraviolet rays having an intensity of 6 μW/cm² at 365 nm were Incidenton the photo-catalytic surface by the white daylight fluorescent lamp.

The rate of decomposition D₁ of hydrogen sulfide except for adsorptionis defined by the following equation.D ₁={(C _(0T) −C _(1T))−(C _(0S) −C _(1B))}/C _(0T)×100(%)As D₁ is larger, the photo-catalytic performance is larger.(3) Weathering Test (Weather Resistance of Film)

A part of the film specimen prepared for the ink color-fading test wasused for the weathering test. The specimen was exposed for 48 hours tolight using Sunshine Super-Long-Life Weather Meter Type WEL-SUN-HCHavailable from Suga Test Instruments Co., Ltd. The weathering test wasconducted according to JIS K7350-4 (Plastic—Weathering Test Method UsingLaboratory LightSource—OpenFlame CarbonArcLamp) using I-type filterunder conditions of black panel temperature: 63±3° C. and water sprayingtime: 18±0.5 minutes/60 minutes.

Gloss of film was measured before and after the film specimen wasexposed to light using Sunshine Super-Long-Life Weatherometer. Themeasurement was carried out by GLOSS CHECKER IC-320 available fromHoriba Ltd. Gloss retention was calculated by the following equation.Gloss retention=BL ₁ /BL ₀×100(%)where BL₀ (%) is gloss of film as measured before light exposure test,and BL₁ (%) is gloss of film as measured after light exposure test.(4) Evaluation of Mixed Crystal State

The mixed crystal state of child particles was evaluated by X-rayphotoelectron spectroscopy (XPS). The details of XPS is described, forexample, in A. Yu. Stakheev et al, J. Phys. Chem., 97(21), 5668-5672(1993).

Example 1

A gaseous titanium tetrachloride having a concentration of 100% byvolume and a gaseous silicon tetrachloride having a concentration of100% by volume were mixed together at a rate of 9.4 Nm³/hour and 0.25Nm³/hour, respectively, and the mixed gas was heated to 1,000° C. Oxygengas and water vapor were mixed together at rate of 8 Nm³/hour and 20Nm³/hour, respectively, and the mixed gas was heated to 1,000° C. Thetwo kinds of mixed gases maintained at that temperature were fed at aflow rate of 49 m/second and 60 m/second, respectively, through aco-axial parallel flow nozzle into a reaction tube so that the titaniumtetrachloride-silicon tetrachloride mixed gas flows through the innertube of the coaxial parallel flow nozzle. The reaction tube had an innerdiameter of 100 mm. The calculated flow rate in the reaction tube at areaction temperature of 1,300° C. was 10 m/second.

Cool air was introduced into the reaction tube so that the residencetime at a high temperature within the reaction tube is not larger than 3seconds. Ultra-fine particles in the reaction product were collected bya polytetrafluoroethylene bag filter, and the thus-collected powder wasdried at 500° C. for 1 hour in an air atmosphere in an oven, anddechlorination treatment was carried out.

The thus-obtained mixed crystal oxide ultra-fine particles had a BETspecific surface area of 24 m²/g, a SiO₂ content of 2.2% by mass and achlorine content of 0.01% by mass, and had an average primary particlediameter of 0.06 μm as calculated from the BET specific surface area.XPS revealed the existence of a titanium-oxygen-silica bond. The mixedcrystal oxide ultra-fine particles were used as child particles for thepreparation of a composite particle as follows.

800 g of alumina balls having a diameter of 5 mm were placed in a nylonvessel having a diameter of 12.5 cm. 190 g of aluminum hydroxideparticles having an average diameter of 85 μm (“Hygilite™ H-10 availablefrom Showa Denko K.K.) and 10 g of titanium dioxide-silica compositefine particles prepared by the above-mentioned process (average primaryparticle diameter as calculated from BET specific surface area; 0.06 μm,SiO₂ content: 2.2% by mass) were placed in the nylon vessel. The lid ofthe vessel was shut down, and the content was mixed and pulverized at 50rpm for 2 hours. The energy constant was 3,000.

After completion of the mixing and pulverization, the content wasobserved by scanning electron microscope. It was found that free fineparticles are present only in a very minor amount and the most part ofparticles were a composite particle. It was confirmed that the compositeparticle was comprised of a mother particle and, supported on thesurface thereof, titanium, dioxide-silica composite fine particles as achild particles. The mother particle of the composite particle was analuminum hydroxide particle having an average diameter of about 60 μm asmeasured by the laser diffraction-scattering particle size measuringmethod. Thus, the particle size of the aluminum hydroxide particle wasreduced only to a minor extent. The diameter of the titaniumdioxide-silica composite fine particles as calculated from BET specificsurface area was the same as that as measured before made Into themother-child composite particle.

A film specimen was prepared from the mother-child composite particle bythe method mentioned above, and an ink color-fading test was conducted.The magenta color substantially disappeared. In contrast, when a controltest was conducted in a dark place for the same time, the magenta colorwas not faded. Thus, the disappearance of magenta color in the filmspecimen according to the present invention was proved to be due to thephoto-catalytic effect. The film exhibited a gloss retention of 90%, andthe decomposition D₀ of hydrogen sulfide except for adsorption was 40%.

Example 2

800 g of alumina balls having a diameter of 5 mm were placed in a nylonvessel having a diameter of 12.5 cm. 190 g of aluminum hydroxideparticles having an average diameter of 9 μm as measured by the laserdiffraction-scattering particle size measuring method (“Hygilite™ HS-320available from Showa Denko K.K.) and 10 g of the titanium dioxide-silicacomposite fine particles prepared in Example 1. The lid of the vesselwas shut down, and the content was mixed and pulverized at 50 rpm for 30minutes, The energy constant was 750.

After completion of the mixing and pulverization, the content wasobserved by scanning electron microscope. It was found that free fineparticles are present only in a very minor amount and the most part ofparticles were a composite particle. It was confirmed that the compositeparticle was comprised of a mother particle and, supported on thesurface thereof, titanium dioxide-silica composite fine particles aschild particles. The particle diameter of the aluminum hydroxide motherparticle as measured by the laser diffraction-scattering particle sizemeasuring method was approximately the same as that as measured beforemade into the mother-child composite particle. The particle diameter ofthe titanium dioxide-silica composite fine particles as calculated fromBET specific surface area was the same as that as measured before madeinto the mother-child composite particle.

A film specimen was prepared from the mother-child composite particle bythe method mentioned above, and an ink color-fading test was conducted.The magenta color substantially disappeared. In contrast, when a controltest was conducted in a dark place for the same time, the magenta colorwas not faded. Thus, the disappearance of magenta color in the filmspecimen according to the present invention was proved to be due to thephoto-catalytic effect. The film exhibited a gloss retention of 80%, andthe decomposition D₀ of hydrogen sulfide except for adsorption was 60%.

Example 3

800 g of alumina balls having a diameter of 5 mm were placed in a nylonvessel having a diameter of 12.5 cm. 190 g of nylon powder comprised ofspherical particles having an average particle diameter of 10 μm and amelting point of 165° C. (“KG-100” available from Toray Industries Inc.)and 10 g of the titanium dioxide-silica composite fine particlesprepared in Example 1. The lid of the vessel was shut down, and thecontent was mixed and pulverized at 50 rpm for 8 hours. The energyconstant was 12,000.

After completion of the mixing and pulverization, the content wasobserved by scanning electron microscope. It was found that free fineparticles are present only in a very minor amount and the most part ofparticles were a composite particle. It was confirmed that the compositeparticle was comprised of a nylon mother particle and, supported on thesurface thereof, titanium dioxide-silica composite fine particles aschild particles. The particle diameter of the nylon mother particle asmeasured by the laser diffraction-scattering particle size measuringmethod was approximately the same as that as measured before made intothe mother-child composite particle. The particle diameter of thetitanium dioxide-silica composite fine particles as calculated from BETspecific surface area was the same as that as measured before made intothe mother-child composite particle.

A film specimen was prepared from the mother-child composite particle bythe method mentioned above, and an ink color-fading test was conducted.The magenta color substantially disappeared. In contrast, when a controltest was conducted in a dark place for the same time, the magenta colorwas not faded. Thus, the disappearance of magenta color in the filmspecimen according to the present invention was proved to be due to thephoto-catalytic effect. The film exhibited a gloss retention of 85%, andthe decomposition D₀ of hydrogen sulfide except for adsorption was 55%.

Example 4

Super-mixer SMG-100 having a volume of 100 liters (available from K.K.Kawata) was charged with 27 kg of calcium carbonate having an averageparticle diameter of 14 μm as measured by the laserdiffraction-scattering particle size measuring method (“Whiton B”available from Shiraishi Calcium Kaisha Ltd.). Then 3 kg g of thetitanium dioxide-silica composite fine particles prepared in Example 1was added. The lid of the vessel was shut down, and the content wasmixed and pulverized at 1,500 rpm for 3 minutes at room temperature. Theenergy constant k2 was 4,500.

After completion of the mixing and pulverization, the content wasobserved by scanning electron microscope. It was found that free fineparticles are present only in a very minor amount and the most part ofparticles were a composite particle. It was confirmed that the compositeparticle was comprised of a calcium carbonate mother particle and,supported on the surface thereof, titanium dioxide-silica composite fineparticles as child particles. The particle diameter of the calciumcarbonate mother particle as measured by the laserdiffraction-scattering particle size measuring method was approximatelythe same as that as measured before made into the mother-child compositeparticle. The particle diameter of the titanium dioxide-silica compositefine particles as calculated from BET specific surface area was the sameas that as measured before made into the mother-child compositeparticle.

A film specimen was prepared from the mother-child composite particle bythe method mentioned above, and an ink color-fading test was conducted.The magenta color substantially disappeared. In contrast, when a controltest was conducted in a dark place for the same time, the magenta colorwas not faded. Thus, the disappearance of magenta color in the filmspecimen according to the present invention was proved to be due to thephoto-catalytic effect. The film exhibited a gloss retention of 85%, andthe decomposition D₀ of hydrogen sulfide except for adsorption was 50%.

Example 5

Paint-shaker having a volume of 5 liters (available from Asada TekkouK.K.) was charged with 1.5 kg of calcium carbonate having an averageparticle diameter of 14 μm as measured by the laserdiffraction-scattering particle size measuring method (“Whiton B”available from Shiraishi Calcium Kaisha Ltd.). Then 200 g of thetitanium dioxide-silica composite fine particles prepared in Example 1was added. The lid of the vessel was shut down, and the content wasmixed and pulverized for 3 minutes at room temperature. The energyconstant k3 was about 600.

After completion of the mixing and pulverization, the content wasobserved by scanning electron microscope. It was found that free fineparticles are present only in a very minor amount and the most part ofparticles were a composite particle. It was confirmed that the compositeparticle was comprised of a calcium carbonate mother particle and,supported on the surface thereof, titanium dioxide-silica composite fineparticles as child particles. The particle diameter of the calciumcarbonate mother particle as measured by the laserdiffraction-scattering particle size measuring method was approximatelythe same as that as measured before made into the mother-child compositeparticle. The particle diameter of the titanium dioxide-silica compositefine particles as calculated from BET specific surf ace area was thesame as that as measured before made into the mother-child compositeparticle.

A film specimen was prepared from the mother-child composite particle bythe method mentioned above, and an ink color-fading test was conducted.The magenta color substantially disappeared. In contrast, when a controltest was conducted in a dark place for the same time, the magenta colorwas not faded thus, the disappearance of magenta color In the filmspecimen according to the present invention was proved to be due to thephoto-catalytic effect. The film exhibited a gloss retention of 80%, andthe decomposition D₀ of hydrogen sulfide except for adsorption was 65%.

Example 6

50 liters of pure water as previously metered (“liter” is hereinafterabbreviated to as “L”) was heated to 98° C. with stirring. At thattemperature, 3.6 kg of an aqueous titanium tetrachloride (available fromSumitomo Titanium K.K.) solution having a titanium concentration of 15%by mass was dropwlse added over a period of 120 minutes. Thus-obtainedwhite turbid slurry was subjected to electric dialysis to be therebydechlorinated to obtain a slurry having a pH value of 4. A part of theslurry was taken and the solid content was measured by a dry constantmass method. The sold content was 2% by mass.

X-ray diffraction analysis of the dry powder revealed that the powderwas predominantly comprised of brookite titanium dioxide. Morespecifically the dry powder contained 89% by mass of brookite titaniumdioxide and 11% by mass of anatase titanium dioxide.

100 g of sodium pyrophosphate (for food additive, available from TaiheiChem. Ind. Co., Ltd.) was dissolved in pure water to prepare 2 kg of anaqueous sodium pyrophosphate solution having a concentration of 5% bymasse.

A reaction vessel was charged with 50 L of the above-mentioned titaniumdioxide slurry having a concentration of 2% by mass while being cooledand stirred. Then 2 kg of the aqueous sodium pyrophosphate solutionhaving a concentration of 5% by mass, and an aqueous sodium hydroxidesolution having a concentration of 5% by mass were added over a periodof 1 hour to prepare an aqueous mixed liquid had a pH value of 8 to 9.The reaction temperature was 20 to 25° C.

The thus-obtained sodium pyrophosphate-containing aqueous titaniumdioxide slurry was maintained at 22 to 28° C. for 1 hour. The electricconductivity of the slurry was 10,000 μS/cm. Then the slurry wasfiltered through a rotary filter press (available from Kotobuki Eng. &Mfg. Co. Ltd.) and washed. Water washing was thoroughly conducted untilthe electric conductivity of the washed slurry reached 50 μS/cm, and theslurry was concentrated to obtain a photo-catalytic slurry. Thephoto-catalytic slurry had a pH value of 7.8 as measured pH meter (D-22available from Horiba Ltd.)

A part of the photo-catalytic slurry was taken and a powder was obtainedby a dry constant mass method. The solid content in slurry was 10% bymass. Fourier transform infrared microscope (FT-IR) (FT-IR 1650,available form Perkin-Elmer Co.) analysis of the dry powder revealed theabsorbance of pyrophosphate. Atomic emission spectrochemioal analysis(ICP) (ICPS-100V, available from Shimadzu Corporation) of the powderrevealed that the contents of Na and phosphorus were 0.7% by mass and1.2% by mass, respectively. Electrophoresis light scattering analysisusing ELS-8000 available from Otsuka Electronics Co., Ltd. to measureζ-potential revealed that the isoelecric point was 2.1. The BET specificsurface area as measured using Flow Sorb II 2300 available fromShimadzu-Corporation was 140 m²/g.

To 10 kg of the above-mentioned photo-catalytic slurry, 70 kg of purewater and 20 kg of calcium carbonate having an average particle diameterof 14 μm as measured by the laser diffraction-scattering particle sizemeasuring method (“Whiton B” available from Shiraishi Calcium KaishaLtd.). The mixture was thoroughly stirred, and then dried by a workingmedia-flowing dryer (slurry drier available from Ookawara Mfg. Co.) toprepare a composite particle comprised of a calcium carbonate motherparticle, and, supported thereon, child particles comprising finetitanium dioxide particles having a Brφnsted acid salt supported on thesurface thereof.

A film specimen was prepared from the mother-child composite particle bythe method mentioned above, and an ink color-fading test was conducted.The magenta color substantially disappeared. In contrast, when a controltest was conducted in a dark place for the same time, the magenta colorwas not faded. Thus, the disappearance of magenta color in the filmspecimen according to the present invention was proved to be due to thephoto-catalytic effect. The film exhibited a gloss retention of 80%. Thedecomposition D₀ of hydrogen sulfide except for adsorption was 75% asmeasured using a black light lamp as light source.

The decomposition D₀ of hydrogen sulfide except for adsorption was 12%as measured using a white daylight fluorescent lamp as light source.Thus decomposition of hydrogen sulfide occurred even when a weakfluorescent lamp was used.

Example 7

To 10 kg of the photo-catalytic slurry prepared in Example 6, 150 kg ofpure water and 40 kg of calcium carbonate having an average particlediameter of 14 μm as measured by the laser diffraction-scatteringparticle size measuring method (“Whiton B” available from ShiraishiCalcium Kaisha Ltd.). The mixture was thoroughly stirred, and then driedby the same procedure as mentioned in Example 6 to prepare a compositeparticle.

A film specimen was prepared from the mother-child composite particle bythe method mentioned above, and an ink color-fading test was conducted.The magenta color substantially disappeared. In contrast, when a controltest was conducted in a dark place for the same time the magenta colorwas not faded. Thus, the disappearance of magenta color in the filmspecimen according to the present invention was proved to be due to thephoto-catalytic effect. The film exhibited a gloss retention of 80%. Thedecomposition D₀ of hydrogen sulfide except for adsorption was 90% asmeasured using a black light lamp as light source.

The decomposition D₀ of hydrogen sulfide except for adsorption was 19%as measured using a white daylight fluorescent lamp as light source.Thus decomposition of hydrogen sulfide occurred even when a weakfluorescent lamp was used.

Example 8

To 10 kg of the photo-catalytic slurry prepared in Example 6, 135 kg ofpure water and 5 kg of calcium carbonate having an average particlediameter of 14 μm as measured by the laser diffraction-scatteringparticle size measuring method (“Whiton B” available from ShiraishiCalcium Kaisha Ltd.). The mixture was thoroughly stirred, and then driedby the same procedure as mentioned in Example 6 to prepare a compositeparticle.

A film specimen was prepared from the mother-child composite particle bythe method mentioned above, and an ink color-fading test was conducted.The magenta color substantially disappeared. In contrast, when a controltest was conducted in a dark place for the same time, the magenta colorwas not faded. Thus, the disappearance of magenta color in the filmspecimen according to the present invention was proved to be due to thephoto-catalytic a effect. The film exhibited a gloss retention of 85%.The decomposition D₀ of hydrogen sulfide except for adsorption was 70%as measured using a black light lamp as light source.

The decomposition D₀ of hydrogen sulfide except for adsorption was 10%as measured using a white daylight fluorescent lamp as light source.Thus decomposition of hydrogen sulfide occurred even when a weakfluorescent lamp was used.

Example 9

The photo-catalytic slurry prepared in Example 6 was dried by a workingmedia-flowing dryer (slurry drier available from Ookawara Mfg. Co.) toprepare child particles. By the same procedures as described in Example4, a composite particle comprised of a calcium carbonate motherparticle, and, supported thereon, child particles comprising finetitanium dioxide particles having a Brφnsted acid salt supported on thesurface thereof.

A film specimen was prepared from the mother-child composite particle bythe method mentioned above, and an ink color-fading test was conducted.The magenta color substantially disappeared. In contrast, when a controltest was conducted In a dark place for the same time, the magenta colorwas not faded. Thus, the disappearance of magenta color in the filmspecimen according to the present invention was proved to be due to thephoto-catalytic effect. The film exhibited a gloss retention of 80%. Thedecomposition D₀ of hydrogen sulfide except for adsorption was 71% asmeasured using a black light lamp as light source.

The decomposition Do of hydrogen sulfide except for adsorption was 12%as measured using a white daylight fluorescent lamp as light source.Thus decomposition of hydrogen sulfide occurred even when a weakfluorescent lamp was used.

Comparative Example 1

Super-mixer SMG-100 having a-volume of 100 liters (available from K.K.Kawata) was charged with 27 kg of calcium carbonate having an averageparticle diameter of 14 μm as measured by the laserdiffraction-scattering particle size measuring method (“Whiton B”available from Shiraishi Calcium Kaisha Ltd.). Then 3 kg g of thetitanium dioxide-silica composite fine particles prepared in Example Iwas added. The lid of the vessel was shut down, and the content wasmixed and pulverized at 200 rpm for 30 seconds at room temperature. Theenergy constant k2 was 100.

After completion of the mixing and pulverization, the content wasobserved by scanning electron microscope. It was found that the contentwas a mere mixture of the calcium carbonate particles and the titaniumdioxide-silica composite fine particles.

A film specimen was prepared from the mixed powder by the methodmentioned above, and an ink color-fading test was conducted. The magentacolor did not disappear. The film exhibited a gloss retention of smallerthan 40%. This poor gloss retention Is believed to be due to the factthat the calcium carbonate mother particle and the titaniumdioxide-silica composite fine particles were not formed into compositeparticles, and thus, the titanium dioxide-silica composite fineparticles were directly contacted with a resin, and thus the weatherresistance of resin was deteriorated by the photo-catalytic, function.

Comparative Example 2

Super-mixer SMG-100 having a volume of 100 liters (available from K.K.Kawata) was charged with 27 kg of calcium carbonate having an averageparticle diameter of 14 μm as measured by the laserdiffraction-scattering particle size measuring method (“Whiton B”available from Shiraishi Calcium Kaisha Ltd.). Then 3 kg g of thetitanium dioxide-silica composite fine particles prepared in Example 1was added. The lid of the vessel was shut down, and the content wasmixed and pulverized at 1,500 rpm for 45 minutes at room temperature.The energy constant k2 was 67,500.

After completion of the mixing and pulverization, the treated particlesstuck to the wall of super-mixer. This is due to the mixing andpulverization treatment was conducted to an undue extent. Theagglomerated particles were difficult to disintegrate, and thus, had nopractical use.

Comparative Example 3

50 L of pure water as previously metered was heated to 98° C. withstirring. At that temperature, 3.6 kg of an aqueous titaniumtetrachloride (available from Sumitomo Titanium K.K.) solution having atitanium concentration of 15% by mass was dropwise added over a periodof 120 minutes. Thus-obtained white turbid slurry was subjected toelectric dialysis to be thereby dechlorinated to obtain a slurry havinga pH value of 4. A part of the slurry was taken and the solid contentwas measured by a dry constant mass method. The sold content was 2% bymass.

X-ray diffraction analysis of the dry powder revealed that the powderwas predominantly comprised of brookite titanium dioxide. Morespecifically the dry powder contained 89% by mass of brookite titaniumdioxide and 11% by mass of anatase titanium dioxide.

A part of the above-mentioned slurry was dried by a workingmedia-flowing dryer (slurry drier available from Ookawara Mfg. Co.) toprepare child particles. By the same procedures as described in Example4, a composite particle comprised of a calcium carbonate motherparticle, and, supported thereon, child particles comprising finetitanium dioxide particles.

A film specimen was prepared from the composite particle y the methodmentioned above, and an ink color-fading test was conducted. The magentacolor substantially disappeared. But, the film exhibited a glossretention of smaller than 30%. This poor gloss retention is believed tobe due to the fact that the child titanium dioxide particles were nottreated with a pyrophosphate and thus were not formed into a compositeparticle with the mother particle. Therefore, the child titanium dioxideparticles were dispersed as they were in a resin, and thus, the weatherresistance of resin was deteriorated by the photo-catalytic function.

Comparative Example 4

To 10 kg of the photo-catalytic slurry prepared in Example 6, 1,000 g ofcalcium carbonate having an average particle diameter of 14 μm asmeasured by the laser diffraction-scattering particle size measuringmethod (“Whiton B” available from Shiraishi Calcium Kaisha Ltd.). Themixture was thoroughly stirred, and then dried by the same procedure asmentioned in Example 6 to prepare a composite particle.

A film specimen was prepared from the composite particle by the methodmentioned above, and an ink color-fading test was conducted. The magentacolor substantially disappeared. But, the film exhibited a very smallgloss retention of 18%.

Field of Utilization in Industry

In the case when the composite particle of the present invention ismixed with an organic polymer to prepare an organic polymer composition,and the composition is shaped, a shaped article exhibiting ultravioletray-screening function can be obtained. The shaped article is in theform of, for example, fiber, film or a plastic molding.

When the composite particle of the present invention is kneaded togetherwith a resin to prepare a film, or it is coated together with a resinbinder on a structure, the resulting film or structure is characterizedin that the particles having a photo-catalytic activity are partiallyexposed on the outside. Therefore, the photo-catalytic activity ofparticles can be sufficiently manifested and the decomposition of theresin constituting the film or coating can be minimized. Thus, the filmor structure has enhanced weather resistance. The film or structure withthe composite particle having a good durability can be made at a lowcost.

In the case when the smaller particles of the composite particle of thepresent invention are titanium dioxide fine particles containing aBrφnsted acid salt or titanium dioxide-silica composite fine particles,the photo-catalytic activity of the film or structure can be manifestedto a satisfying extent even when light is weak, for example, in theroom.

1. A composite particle comprised of a larger particle and, supportedthereon, smaller particles wherein the smaller particles arephotocatalyst-containing fine particles having an average particlediameter in the range of 0.005 μm to 0.5 μm as calculated from a BETspecific surface area, and the larger particle has an average particlediameter in the range of 2 μm to 200 μm as measured by the laserdiffraction-scattering particle size measuring method.
 2. The compositeparticle according to claim 1, wherein the smaller particles comprisetitanium dioxide as a photocatalyst.
 3. The composite particle accordingto claim 1, wherein the smaller particles are composite particlescomprising titanium dioxide and an inorganic compound exhibiting nophoto-catalytic activity.
 4. The composite particle according to claim3, wherein the inorganic compound exhibiting no photo-catalytic activityis silica and the content of silica in the smaller particles is at least0.5% by mass but not larger than 50% by mass, based oln the mass of thesmaller particles.
 5. The composite particle according to claim 1,wherein the smaller particles contain a Brφnsted acid salt.
 6. Thecomposite particle according to claim 5, wherein the smaller particlesare titanium dioxide particles containing the Brφnsted acid salt on thesurfaces of particles.
 7. The composite particle according to claim 6,wherein the Brφnsted acid salt is a condensed phosphate.
 8. Thecomposite particle according to claim 5, wherein the smaller particlescontain the Brφnsted acid salt in an amount in the range of 0.01% bymass to 50% by mass.
 9. The composite particle according to claim 2,wherein the titanium dioxide comprises a brookite crystalline phase. 10.The composite particle according to claim 1, wherein the larger particleis a spherical resin particle having a melting point of at least 150° C.11. The composite particle according to claim 1, wherein the largerparticle is comprised of a hydroxide, oxide or carbonate, which containsat least one kind of element selected from the group consisting ofaluminum, magnesium, calcium and silicon.
 12. The composite particleaccording to claim 1, wherein the amount of smaller particles is in therange of 0.5% by mass to 40% by mass based on the mass of the largerparticle.
 13. A method of producing a composite particle as claimed inclaim 1, comprising dry-mixing the smaller particles and the largerparticle by a ball mill, characterized in that the dry-mixing is carriedout under conditions such that k value as defined by the followingequation (1) is in the range of 50 to 50,000,k=(wm/wp)×d×n×t   equation (1): where k is energy constant fordry-mixing, wp is total mass (g) of particles to be dry-mixed, wm ismass (g) of mixing media, d is inner diameter (m) of ball mill, n isnumber of rotation (rpm) of ball mill, and t is time (min) fordry-mixing.
 14. A method of producing a composite particle as claimed inclaim 1, comprising mixing, pulverizing and stirring the smallerparticles and the larger particle by a powder-treating apparatusprovided with rotary blades, characterized in that the mixing,pulverizing and stirring are carried out under conditions such that k2value as defined by the following equation (2) is in the range of 250 to50,000,k2=n×t   equation (2): where n is number of rotation (rpm) of rotaryblades, and t is time (min) for mixing, pulverizing and stirring.
 15. Amethod of producing a composite particle as claimed in claim 1,comprising mixing, pulverizing and stirring the smaller particles andthe larger particle by a shaking-type powder-treating apparatus,characterized in that the mixing, pulverizing and stirring are carriedout under conditions such that k3 value as defined by the followingequation (3) is in the range of 50 to 50,000,k3=n×t   equation (3): where n is number of shaking per minute, and t istime (min) for mixing, pulverizing and stirring.
 16. A organic polymercomposition comprising an organic polymer and a composite particle asclaimed in claim 1, wherein the amount of the composite particle is inthe range of 0.01% to 80% by mass based on the total mass of the organicpolymer composition.
 17. The organic polymer composition according toclaim 16 wherein the organic polymer is at least one kind of resinselected from the group consisting of synthetic thermoplastic resins,synthetic thermosetting resins and natural resins.
 18. The organicpolymer composition according to claim 16, wherein the organic polymercomposition is a compound.
 19. The organic polymer composition accordingto claim 16, wherein the organic polymer composition is a master batch.20. A shaped article made by shaping an organic polymer composition asclaimed in of claim
 16. 21. A coating composition comprising a compositeparticle as claimed in claim
 1. 22. A paint composition comprising acomposite particle as claimed in claim
 1. 23. A structure comprising ona surface thereof a composite particle as claimed in claim
 1. 24. Acosmetic composition comprising a composite particle as claimed inclaim
 1. 25. A fiber comprising a composite particle as claimed inclaim
 1. 26. A film comprising a composite particle as claimed in claim1.